The study has 2 specific aims; the first aim is to determine the contribution of amino acids (AA) to the obligatory N loss as fuel and as metabolic precursors. In this aim investigators will try to 1) minimize the utilization of amino acids as fuels between meals by frequent administration of carbohydrate (CHO), and 2) suppress AA oxidation during muscular activity by either providing CHO or inhibiting muscular activity by tranquilizers, 3) replace the limiting AA in protein turnover and their keto derivatives and 4) establish a protocol for minimum N waste with protein-free diets. The second aim is to understand why meal feeding of protein is inefficient. The investigators observed that casein feeding replenishes the liver protein efficiently, but not the muscle protein. They now will investigate a) how much of the protein-sparing effects of carbohydrates is due to insulin and how much to substrate competition, b) if glucagon interferes with hepatic protein replenishment, c) if IGF-1 improves protein replenishment in the muscle, d) if the hepatic protein replenishment depends upon the portal AA availability, and the combination of AA or keto derivatives which achieve maximal hepatic protein deposition.